The aliphatic polyamides frequently referred to as nylons form an important group of synthetic polycondensation polymers. They are linear molecules that are semi-crystalline and thermoplastic in nature. They are important and versatile industrial materials because of their superior physical and mechanical properties, namely relatively higher melting points and heat resistance, abrasion resistance, chemical inertness, high modulus, ease of processing, hydrophilicity, superior yield and high level of purity after production [1-8].
These above-mentioned properties of the polyamides stem mainly from their capability to form intramolecular and intermolecular hydrogen bond structures between the amide (—NH—) and carbonyl (—CO—) functional groups, also known as the carbonamide functional moiety, within and between the linear chains in the polyamide crystal respectively [9-12]. A representation of the hydrogen bond interaction between the carbonyl and amide functional groups within the polyamide chain is shown in FIG. 1. The hydrogen bonds are able to retain the molecular chains in an ordered, solid phase before and even after the alkane segments have effectively melted [10]. The length and strength of the hydrogen bond structures are dependent on the polyamide type and the method of synthesis leaving each with slightly different properties [3, 6-11]. The polyamides consist of amide groups separated by alkane segments (FIG. 1) and the number of carbon atoms separating the nitrogen atoms defines the particular nylon type [3, 8, 9]. Cui and co-workers (2004) have successfully subdivided polyamides into six categories namely: even-even, odd-odd, odd-even, even-odd, even and odd [9].
In the present study, the even-even polyamides were selected because of their well-defined structural arrangement due to the fully formed, saturated hydrogen bonds between the molecular chains. This class forms chain-folded sheets and the hydrogen bonds formed between the amide groups in adjacent chains within these sheets provides them with good fiber-forming properties. At room temperature, parallel layers usually form (no inter-sheet hydrogen bonding) that have extended conformations. These sheets can either be stacked together with a progressive shear termed the α-phase or with a staggered shear termed the β-phase giving different triclinic unit cells [7, 11, 12]. Even-even polyamides such as polyamides 6,6; 12,10; 4,8; 4,10; 4,12; 6,10; 6,12; 6,18 and 8,12 have been widely investigated and used in industry [1-21]. Thus far, the investigations concentrated extensively on the characterization of the physicochemical behavior with not much emphasis (when compared with the physicomechanical characteristics) on their performance which is highly responsible for majority of their applications [7, 11-20]. Thus far mechanical assessments conducted on pure polyamides and their blends with other polymeric materials have been in the form of tensile testing, dynamic mechanical analysis and ductility [7, 13, 16, 17].
As far as we know, no study relating the influence of monomeric concentrations and solvent volume ratios to the physicochemical and physicomechanical properties of polyamides using textural profile analysis (TPA) as well as using a modified interfacial polymerization approach to synthesize polyamide variants to develop a rate-modulated monolithic matrix drug delivery system has been reported. Rate-modulated drug delivery technology represents one of the emerging and challenging frontier areas of research in modern medicine and pharmaceuticals [37]. One of the challenging fields of such research is in the fabrication of novel monolithic polymeric systems, using simple process or material modifications such as altering the type of polymer employed during formulation, which has the ability to provide flexible yet rate-modulated drug release performance in a predictable manner achieving more effective therapeutic outcomes and eliminates the risk of both under- and over-dosing.